1. Field of the Invention
The present invention relates to a method and a device for controlling the braking system of a vehicle having a vacuum brake booster and a vacuum source.
2. Description of Related Art
It is known from published German patent document DE 195 24 939 that one may control the braking system of a vehicle in such a way that, in certain operating situations, the brake force is built up beyond the actual driver specification at the wheel brake. Such an operating situation exists, for example, when the driver operates the brake pedal very rapidly. The operation of the brake pedal results in a change in the admission pressure, that is, the pressure that exists at the output of the main brake cylinder. Therefore, it is checked at one control unit whether the change in the admission pressure caused by the brake pedal operation is exceeding a certain threshold. When the triggering threshold is exceeded, an automatic braking procedure (emergency or panic braking) is triggered. For the improvement of the triggering criterion it is provided that one should select the threshold value as a function of different operating variables, such as, for instance, the admission pressure level, the vehicle speed or the vehicle rotation rate.
It is also known from published German patent document DE 197 39 152 that one may determine the triggering threshold value as a function of the currently present braking phase. In this context, a control unit decides whether there is an initial braking phase or an ongoing braking process. Different characteristics curves are drawn upon to determine correction factors, depending on the braking phase.
It is true that the known design approaches yield satisfying methods and devices for determining a triggering threshold value which is used for triggering an automatic braking procedure. However, it turns out that the determination of the threshold value does not take into account all the important operating variables. In the case of highly dynamic pedal operation, that is, for instance, during cadence braking, the admission pressure that sets in after a brake pedal operation, that is, the admission pressure level and the resulting admission pressure gradient, fall off with an increasing number of brake pedal operations. If the control unit uses the gradient of the admission pressure and/or the admission pressure level as the signal characterizing the operation of the brake pedal, this has the result that, after a large number of pedal actuations, a specified triggering threshold value is no longer able to be exceeded, with the result that an emergency brake situation is no longer reliably detected.